In the case of such heavy duty link pin it is frequently necessary to remove a pin of several centimeters diameter that extends between bosses, in which it is an interference fit, spaced apart by tens of centimeters.
It is known to employ differential heating to the link pin and bosses to reduce the axial force required by a simple apparatus but such differential heat is difficult to effect and, if the pin is to be removed due to a defect in pin or boss that requires metallurgical examination, such application of heat would be inappropriate.
It is known to displace a link pin from a chain by means of an elongate drift pin of similar length, the drift pin being driven by an axially applied force by a rectilinearly stroked ram.
However, in the case of long link pins to which large forces have to be applied such an arrangement is impractical, both in terms of the difficulties in producing large forces and long strokes from ram means and the difficulties of ensuring that forces applied at the distant end of a long drift have no off-axis components which could lead to bending of the drift pin or even destruction of the apparatus and danger to personnel.
To avoid the stroke length difficulty a short stroke ram means could be employed and repositioned after each stroke, but the undesirability of applying large forces at the distant end of the drift still remains.
It is also known to apply axial force to such a long drift by means of a rotary transducer and screw thread connection which converts rotatary motion into axial force, but the force is still applied at the end of a long drift.
Although such apparatus is suited to inserting a link pin by substituting it for a drift used in extraction of a link pin, it will be appreciated that the forces involved in inserting a new link pin are usually lower than those of extracting an old one and that extraction, which is often conducted under unfavourable conditions and with inadequate space, may not be feasible with apparatus of such length.